1. Field
The present invention relates generally to data communication, and more specifically to techniques for detecting received messages when one or more signaling characteristics of the messages are not known a priori. The techniques may be used for blind transport format detection (BTFD) in a W-CDMA system and blind rate detection in an IS-95 CDMA system.
2. Background
Wireless communication systems are widely deployed to provide various types of communication such as voice, packet data, and so on. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), or some other multiple access techniques. CDMA systems provide certain advantages over other types of system, including increased system capacity.
For enhanced flexibility and better utilization of the available system capacity, some communication systems transmit data using a signaling scheme that supports a number of different rates or transport formats. For example, in an IS-95 CDMA system, data may be transmitted at one of four possible rates (i.e., full, half, quarter, and eight rates), with the rate being selected for each frame based on the amount of data to be transmitted. In particular, data may be sent using full rate during periods of active speech and eighth rate during periods of silence (i.e., pauses). In a W-CDMA system, data may be transmitted using one of a number of supported transport formats, again depending on the amount of data to be transmitted.
To minimize overhead, no signaling may be sent to indicate the particular rate or transport format being used for a particular frame. In this case, the receiver needs to perform “blind detection” of each received frame to recover the transmitted data. Since each frame is typically received in the presence of noise, the ability to determine which one of the possible rates or transport formats used for the frame may be compromised.
As can be seen, there is a need in the art for techniques to accurately detect received frames in which one or more signaling characteristics (e.g., rate or transport format) of the frames are not known a priori.